CHAP, ii.] RESPIRATION. 607 



eral resistance by slackening of the vaso-constriction is shewn 

 by the fact that if the artificial respiration be resumed while 

 this fall is taking place, or when it has taken place, the pres- 

 sure at once rises again very rapidly as the heart recovers its 

 power, shewing that the vaso-constriction is still at work. 

 The diminished energy of the heart beat is due to the nutrition 

 of the cardiac tissue suffering under the increasing venosity of 

 the blood, and if the air continue to fail to get access to 

 the blood in the lungs, the heart finally ceases to beat. The 

 right side, by virtue of what appears to be an inherent quality, 

 continues to beat rather longer than the left; but the 

 pulmonary peripheral resistance continuing, the efforts of the 

 right ventricle to empty itself are ineffectual; and at death it 

 is the right side which is especially distended. 



In an animal, not under urari, and dying by asphyxia in an 

 ordinary way, the phenomena are in the main the same as those 

 of which we have just given a sketch; but as we have said the 

 exaggerated respiratory movements, and especially the convul- 

 sive struggles, in which these culminate, introduce complica- 

 tions. Perhaps the most marked of these is the increased 

 venous inflow to the right side of the heart, of which these 

 movements are the cause, for as we have seen all the move- 

 ments in question augment the flow along the veins to the 

 heart. But the pulmonary peripheral resistance is a bar to 

 the progress to the left side, and hence the right side becomes 

 increasingly distended. 



During asphyxia, under urari, the blood-pressure curve 

 shews other certain interesting features deserving of attention. 



Upon the cessation of the artificial respiration, the respiratory 

 undulations of course cease also, so that the blood-pressure curve 

 rises at first steadily broken only by the heart-beats ; yet after 

 a while new undulations, the so-called Traube or Traube-Hering 

 curves, make their appearance (Fig. 100, 2, 3), similar to the 

 previous ones, except that their curves are larger and of a more 

 sweeping character. These new undulations, since they appear 

 in the absence of all thoracic or pulmonary movements, passive 

 or active, and are witnessed even when both vagi are cut, must 

 be of vaso-motorial origin ; the rhythmic rise must be due to a 

 rhythmic constriction of the small arteries; and this probably is 

 caused by a rhythmic discharge from vaso-motor centres, and 

 especially from the bulbar vaso-motor centre. The undula- 

 tions are maintained so long as the blood-pressure continues to 

 rise. With the increasing venosity of the blood, the vaso-motor 

 centres become enfeebled and the undulations disappear. 



We may here incidentally remark that the occurrence of 

 long slow undulations is not dependent on the cessation of the 

 respiratory movements, and on an abnormally venous condition 

 of the blood. They are sometimes (Fig. 101) seen in an animal 



